I would say it depends on your level and how much you can understand. If you find it impossible to understand without subtitles, watch with subtitles. You will learn vocabulary this way as well as getting more comfortable with accents and colloquial speech, and understanding more and more. As soon as you begin to get more comfortable, challenge yourself by watching without the subtitles. When you don't understand something, go back and work out what was said and switch the subtitles on if necessary to make sure you got it all. I would also recommend listening to podcasts and audio books (depending on your level). If you listen to the radio, news for example, so that you already have an idea of what is being talked about, you will find it massively helpful for your comprehension. Listen to the radio all the time and you will find your ears get used to hearing English!

Use subtitles once when you didn't understand a phrase

I think the ones with subtitles help better, then later on when you become familiar with the sounds, you can shift to those without subtitles.

both are useful. Having english subtitles will help if what you are watching contains a lot of new words for you. If you have a rich vocabulary, then go for movies without subs.